This invention relates to sensing devices which utilize the gyroscopic principle, i.e., measuring the Coriolis force created by the conservation of momentum of a moving body. Specifically, the invention concerns devices called micro-gyros, which are small and inexpensive. They rely on conservation of momentum of a structure having limited oscillation motion. They are able to withstand rough environments for long periods of time.
In this field, the terms used to describe the directions of motions and of forces can be confusing. Applicant in describing and claiming the present invention will refer to the three separate directions (which are orthogonally related to one another) as follows: (a) the driven element, which is caused to oscillate (vibrate) at a predetermined, arbitrary rate inside the gyro, moves in a linear drive direction; (b) the velocity of the gyro environment, which is to be determined by the gyro, is around the rate axis; and (c) the Coriolis force, which is a function of the velocity of the gyro environment, is measured by motion of a sensing element in an output direction.
Common assignee Application Ser. No. 08/870,812 relates to a micro-gyro which "separates the mass (momentum of inertia) of the constant motion element driven to oscillate around the drive axis from the mass (momentum of inertia) of the variable motion sensing element which creates the measured force". It accomplishes that result by "using: (a) an outer ring-shaped element which oscillates around the drive axis, and (b) an inner disk-shaped element which oscillates, or rocks, around the output axis as a result of the Coriolis effect". Its dual-element structure "permits the ring and the disk to be excited independently, so that each can be dynamically compensated for manufacturing tolerances by counterbalancing".
Lutz U.S. Pat. No. 5,604,312 shows a rate-of-rotation sensor which uses "an oscillatory mass" moving in a linear vibrating direction, and "a deflectable mass" caused by Coriolis force to move in a linear vibrating direction perpendicular to the motion of the oscillatory mass. Measurement of the Coriolis effect is used to determine angular velocity of the entire sensor around a rate axis, which is perpendicular to the linear vibrating directions of both masses.
The micro-gyro of the common assignee application is able to determine the external rate of rotation around either of the two (X and Y) axes which lie in the plane of the micro-gyro, but not around the third (Z) axis, which is perpendicular to the plane of the micro-gyro. The micro-gyro of the present application, like the sensor of the Lutz patent, is able to determine rate of rotation around the Z-axis, which is perpendicular to the plane of the micro-gyro.